Ordered this with HMF Performance Series pipe on my wife's 2006 trx 450er and it performed killer. We got Sound tested by the U.S. Forest Rangers last week at Coos Bay bay. the pipe with the power core insert registered 85db and the limit was 93db at the time. the quad performed really well with this set up after being jetted with the dyno jet kit. it gave real strong performance over stock.